Described below are a method for operating an electric arc furnace and a smelting plant with an electric arc furnace operated in accordance with this method.
In an electric arc furnace, pieces of material to be smelted, in general steel scrap, if necessary together with further supplementary materials, are melted down by an electric arc which is struck between the material to be smelted and at least one electrode. For this purpose, electrical energy, which is converted into the low voltage range by a so-called furnace transformer, is fed to the electric arc furnace from a medium- or high-voltage supply. From this furnace transformer, the energy is fed to the electrode via a high current system. The scrap metal present in the furnace vessel is melted down by an electric arc which then burns at the tip of the electrode.
The plant components which relate to the supply of electrical energy for the electric arc furnace include a so-called furnace substation, a furnace transformer and a high current system which, for example, incorporates current-conducting height-adjustable supporting arms, to which are attached the electrodes. The height setting of the electrodes, and thereby the energy input into the goods to be smelted, is regulated by an electrode regulation system. This produces a wide selection of working points, or operating conditions, which can differ substantially in terms of the performance demands on the plant components.
The design and selection of the plant components is generally effected on the basis of values from experience for the electric arc furnace concerned. Thus, for example, the design of the furnace transformer is determined as a function of the size of the electric arc furnace, the nature of the steel scrap and the desired productivity, i.e. the smelting capacity (mass of the steel scrap to be melted down per unit time), which determines the required smelting time of the electric arc furnace. In doing this, apart from determining the complex power in the range up to about 300 MVA, the number of stages and the voltages of the stages in the furnace transformer, for example eighteen stages with voltages of up to about 1500 V, and the currents, which can be up to about 100 kA, are defined.
However, in order to reliably avoid damage to those plant components which affect the operating conditions of the electric arc furnace, in particular the furnace transformer, the potential power which is actually available, at least for short periods, is not utilized to the full extent possible, and correspondingly allowance is made for a reduced productivity.